ATS645LSH datasheet(11/14 Pages) ALLEGRO

11 / 14 page

True Zero Speed Miniature Differential Peak-

Detecting Gear Tooth Sensor

ATS645LSH

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

SENSOR OPERATION

Each operating mode is described in detail below.

Power-On

When power (VCC > VCCMIN) is applied to the device, a short

period of time is required to power the various portions of the

IC. During this period, the ATS645 is guaranteed to power-on in

the high current state, ICC(High).

Initial Offset Adjust

The sensor intially cancels the effects of chip, magnet, and

installation offsets. Once offsets have been cancelled, the digital

tracking DAC is ready to track the signal and provide output

switching. The period of time required for both Power-On and

Initial Offset Adjust is deﬁned as the Power-On Time.

Calibration Mode

The calibration mode allows the sensor to automatically select

the proper signal gain and continue to adjust for offsets. The

AGC is active, and selects the optimal signal gain based on the

amplitude of the VPROC signal. Following each adjustment to

the AGC DAC, the Offset DAC is also adjusted to ensure the

internal analog signal is properly centered.

During this mode, the tracking DAC is active and output switch-

ing occurs, but the duty cycle is not guaranteed to be within

speciﬁcation.

Diagnostics

The regulated current output is conﬁgured for two wire appli-

cations, requiring one less wire for operation than do switches

with the more traditional open-collector output. Additionally,

the system designer inherently gains diagnostics because there

is always output current flowing, which should be in either of

two narrow ranges. Any current level not within these ranges

indicates a fault condition.

Running Mode

After the initial calibration period, CI, during which a signal

gain is established, the device moves to Running mode. During

Running mode, the sensor tracks the input signal and gives an

output edge for every peak of the signal. AOA remains active to

compensate for any offset drift over time.

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